Transcript Ingen lysbildetittel

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Optical Transport Network (OTN)
ITU-T standard G.709
Paper: Andreas Schubert: ”G.709 – The Optical
Transport Network (OTN)”
http://www.jdsu.com/productliterature/g709otn_wp_opt_tm_ae.pdf
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Overview
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Literature
Motivation for an optical transport network standard
Properties of OTN
G.709 Interface standard
OTN framing structure - whats the point of all this overhead.
Tandem connection monitoring
Forward Error Correction (FEC)
OTN switching
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Literature
• ITU-T
– G.709 “Interface for the optical transport network (OTN)”
• The most referenced standard in OTN
• Describes Intra and inter –domain interfaces
• Framing and framing structure
– G.872 - Architecture of optical transport networks
• Described from a network level viewpoint
• Describes network layers
• Andreas Schubert “White paper”
– What is a white paper?
– G.709 - The Optical Transport Network (OTN)
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Why not IP directly over WDM?
• IP-WDM, a buzzword from the late 90’s
• Can you transport an IP-packet directly on a fiber?
• Which functionality is required?
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Why not IP directly over WDM?
• IP-WDM, a buzzword from the late 90’s
• Can you transport an IP-packet directly on a fiber?
• Which functionality is required?
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1 Clock information
2 Start/stop indication of packet
3 Error checking?
4 Error correction?
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Functionality added to IP for
WDM transport
• Framing for the physical layer transport
– May e.g. be Ethernet
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Monitoring of errors and signal quality
Management for provisioning of data-paths
Fault handling, fast protection
Management of wavelengths
Management of optical network elements
– Functionality at the physical layer
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Why OTN?
• Standard for optical networks required
– Optical interconnection between equipment from different vendors
– Optical interconnection between different operators
• Once called “digital wrapper”
• Framing of client signal of different protocols for transport over
the physical optical layer
– E.g. IP/Ethernet or IP/ATM or SDH
• Takes SDH/SONET further, enabling optical functionality
– From a single to multiple wavelengths
– Forward Error Correction (FEC)
– What is FEC?
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Properties of OTN
• Protocol transparency
– Handles “any” protocol-stack and gives a physical layer to higher
layer protocols like e.g. IP
• Backward compatibility for existing protocols
– Handles both SDH and Ethernet
• FEC
– Reduces cost, improves performance
• Reduction of 3R regeneration
– Allows management of all-optical network elements
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Interfaces
• Inter-domain interfaces (IrDI)
– Location between networks of two operators
– Location between sub-networks of two vendors in the same
operator domain
– The location within the sub-network of one vendor
– 3R regeneration – Why?
• Intra-Domain interfaces (IaDI)
– The location between the equipment of an individual
manufacturer’s sub-network
– Transparent network
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Inter and intra -domain
• Intra- IaDI within e.g. an operator
• Inter- IrDI between operators or connection to e.g. a
customer (client)
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Transport of a client signal
• Over-Head (OH) added to form optical channel
payload unit (OPU)
• OH to OPU forming optical channel data unit (ODU)
• Additional OH plus FEC are added to form the optical
channel transport unit (OTU)
• Adding further OH creates an OCh which is carried
by one color (wavelength)
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OTN layer structure
• OCh = Optical channel
• OMS = Optical Multiplex section
• OTS = Optical Transmission Section
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OTN hierarchy
OH
OH
OH
Client
Client
Client
OPU
ODU
OPUk
ODUk
FEC
OChannel
Non
Associated
overhead
OCh payload
OCCp OCCp OCCp
OCCp OCCp
OMS payload
OTS payload
OTU
OCC
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In-band and out of band OH
• Non-associated OH (out of band) may be added to
OCh enabling management of multiple colours in
OTN.
• Optical Multiplex Section (OMS)
– Multiplex of OCh’s
• Optical Transmission Section (OTS)
– The transmission medium, I.e. the fibre
Optical channel structure (OCh)
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FAS
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OTU-OH
ODU-OH
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OPU-OH
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Client
FEC
PSI
RES
TCM3
GCC1
TCM6
TCM/ACT
TCM2
GCC2
APS/PCC
TCM5
TCM1
4080
TCM4
FTFL
EXP
PM
RES
PT
RES
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Optical Payload Unit (OPU)
PSI
• Framing of client signal
– May be of any protocol, e.g. SONET/SDH, GFP, IP, GbE
• Payload Structure Identifier (PSI)
– 256 Byte message
– Justification bits for asynchronous mapping of client signal
– PSI0 contains Payload Type (PT) (single byte) identifying type of
payload
– RES – Bytes Reserved for future use
PT
RES
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Optical channel Data Unit (ODU)
functionality
• Tandem Monitoring (TCM)
– Hierarchical error checking using parity bytes
– Allows up to six tandem connections, nesting and overlapping
• Path Monitoring (PM)
– Monitoring of particular sections
– Fault location
• General Communication Channels (GCC)
– Typically Management communication
• Automatic Protection Switching (APS)
– Protection switching at one or more levels
– What is protection switching?
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ODU-k: Defined for several bitrates
• -k is a number defining the bitrate
• Originally defined bitrates
– ODU1: 2.5 Gb/s
– ODU2: 10 Gb/s
– ODU3: 40 Gb/s
• Recently defined/to be defined
– ODU0: 1 Gb/s (Matches Gigabit Ethernet)
– ODU4: 100 Gb/s (Matches 100 Gigabit Ethernet)
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ODU in OTN hierarchy
OH
OH
OH
Client
Client
Client
OPU
ODU
OPUk
ODUk
FEC
OChannel
Non
Associated
overhead
OCh payload
OCCp OCCp OCCp
OCCp OCCp
OMS payload
OTS payload
OTU
OCC
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ODU OH
RES
TCM3
GCC1
TCM6
TCM/ACT
TCM2
GCC2
TCM5
TCM1
TCM4
EXP
PM
APS/PCC
FTFL
RES
• PM - Path Monitoring, contains three sub-fields
• TCM1-TCM6
– OH for six independent TCM’s
– Contains similar sub-fields as PM
• TCM/ACT Activation/deactivation of TCM
• GCC
– Communication between network elements (management), two channels
• APS/PCC
– Automatic Protection Switching
– Protection Communication Channel
• RES Reserved for future use
• EXP Experimental use
• FTFL - Fault Type and fault location Channel
– Fault status, type and location
– Related to TCM span
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Tandem Connection monitoring
• Six levels, nested or cascaded connections
• Nested: A1-A2/B1-B2/C1-C2 and A1-A2/B3-B4
Cascaded: B1-B2/B3-B4
• Carriers may maintain their own service level
agreement (SLA)
– What is a SLA?
Figure from
G.709 standard
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TCM and PM overhead structure
Trail-Trace
Identifier
TTI BIP-8
Maintenance
Signal present
Parity
Source access
Point Identifier
Destination
access
Point Identifier
SAPI
BEI
BDI
STAT
PM
BEI
BDI
STAT
TCM
DAPI
Operator
specific
- Country of origin
- Network operator
- Administrative details
Backward
Error
Indication
Info.
Signal
failure
Upstream
Single bit
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FTFL sub-fields
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Fault status information
Type and location of fault
Related to TCM span
Codes specified: No fault, Signal fail, signal degrade
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Optical channel transport unit (OTU)
• Support transport of OTU via one or more optical
channel connections
• Frame alignment Signal (FAS)
– Multi Frame Alignment Signal (MFAS)
– ODU frames may span multiple OTU frames
– TTI and TCM-ACT (activation) signals requires multiple ODUframes for being processed
• Forward Error Correction (FEC)
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OTU OH structure
FAS
FAS
OTU
MFAS
Comm. OTU
term. Points
(management)
SM
GCC
RES
REServed
Section
For future use
Monitoring
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PM + IAE bit
IAE: Ingress inform egress
Incoming Alignment
error on signal
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Forward Error Correction (FEC)
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FAS
14151617
OTU-OH
ODU-OH
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OPU-OH
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Client
Added at the end of the OTU-frame
Very important property of OTN, why?
Detection of errors
Correction of errors through redundant information
Allows lower signal quality
I.e. allows larger degradation by physical
impairments
4080
FEC
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Physical impairments to be
compensated
• Linear (explain these)
– Attenuation
– Noise
– Dispersion: Chromatic, mode and polarisation
• Non-linear
– Four wave mixing
– Self phase modulation
– Cross phase modulation
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FEC gain
• Bit Error Rate (BER) improvement example: 10-4 ->
10-15
• How can BER be defined, and how is it measured?
• Gain in power level approx 5 dB for 7 % FEC
• Reduce amount of 3R regenerators
• Use existing 2.5 Gb/s links for 10 Gb/s
• Early warning when degradation of link quality start to
appear
• Longer spans between amplifiers in subsea-systems
(lower cost)
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FEC algorithms
• Performance increase depends on algorithm and
amount of overhead (redundancy information)
• Standardized algorithms, G.709. Reed-Solomon
based
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OTN switching
• Client signals of different bitrates can be multiplexed
into higher bitrate OTN signal.
• Switching down to Gigabit granularity (ODU-0)
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Summary OTN
• Management to the high bandwidth WDM network
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SDH/SONET single wavelength, OTN – multiple wavelengths
Builds on management functionality from SDH/SONET
Monitoring functionality
GCC channels for management communication
• Transparency to other protocols, e.g. IP
– Wrap whatever you like
• FEC compensates physical impairments, increases costefficiency
• OTN switching is being deployed
• OTN transmission and switching market is increasing rapidly